The present invention relates to a semiconductor device and a manufacturing technology thereof. In particular, the invention pertains to a technology effective when applied to a power semiconductor device having a package formed by bonding a semiconductor chip onto a die pad portion of a lead frame via a conductive adhesive.
A power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) to be used for a power control switch or a charge/discharge protection circuit switch of portable information devices is sealed in a small surface mount package such as SOP8.
Such a surface mount package for power semiconductor devices has, for example, the following structure. Described specifically, a semiconductor chip having a power MOSFET is mounted, with its main surface up, over a die pad portion formed integrally with a drain lead and adhered onto a die pad portion via a conductive adhesive such as Ag paste. Over the back side of the semiconductor chip, a drain electrode coupled to the drain of the power MOSFET is formed. On the other hand, over the main surface of the semiconductor chip, a source pad and a gate pad are formed. The source pad has a wider area than the gate pad in order to reduce the on resistance of the power MOSFET. The source pad and the gate pad are each electrically coupled to a lead via an Au wire. These members (die pad portion, semiconductor chip, Au wire, and lead) are sealed with a molding resin.
Investigation results on the use, as a conductive adhesive for power semiconductor devices, of a nano-composite Ag paste material formed by mixing Ag nanoparticles with a conventional Ag paste are reported in the proceedings of the 11th Symposium on “Microjoining and Assembly Technology in Electronics”, 233-238 (February, 2005).
Japanese Patent Laid-Open No. 2005-277168 discloses a package for power semiconductor devices in which a source pad of a semiconductor chip is electrically coupled to a lead via a plate-like clip made of copper or a copper alloy. In the package disclosed therein, the source pad and the clip, and the lead and the clip are adhered via a conductive adhesive. The conductive adhesive contains conductive particles made of aluminum or indium having plasticity in a binder resin and is characterized by that the particle size of a part of the conductive adhesive prior to plastic deformation by adhesion is greater than the maximum distance between the source pad and the clip and the maximum distance between the lead and the clip to be adhered.